MERCURY DETERMINATION BY CV-AAS IN WASTE-WATER AND SEWAGE-SLUDGE FROMA STABILIZATION POND SYSTEM

The mercury concentrations in wastewater and sewage sludge of a stabil ization pond system have been evaluated. The system is built by three parallel facultative ponds followed by two systems of three maturation ponds in series. The samples of wastewater and sludge were digested u sing nitric acid and placed into a Parr-type bomb for 4 h at 110 degre es C. Mercury was measured by Cold Vapour Atomic Absorption Spectromet ry (CV-AAS) at 253.7 nm with sodium tetrahydroborate as reductant. The methodologies were checked with an USEPA quality control sample, a st andard reference material from NIST and with another method of mineral ization (cold mineralization) showing good results. Concentrations of mercury in wastewater between 1.47 +/- 0.75 mu g l(-1) have been found at the entrance of the system and 0.74 +/- 0.0 mu g l(-1) at the exit , while in sludge the results were between 0.29 +/- 0.12 mu g kg(-1) i n the facultative pond and 0.04 +/- 0.02 mu g kg(-1) in the second mat uration pond (exit).